This application is a continuation of U.S. patent application Ser. No. 179,428, filed Apr. 8, 1988 abandoned.
1. Field of the Invention
The present invention relates to knee prostheses. More particularly, the invention relates to a replacement system of the tibial component of a knee prosthesis which includes the use of inserts adapted to engage the undersurface of the tibial portion of the knee prosthesis to accommodate bony defects on the upper portion of the tibia.
2. General Background
In the total replacement of a knee joint, a knee prosthesis includes an upper femoral component which is a component secured to the upper femoral condyles that have been prepared and sculptured to secure the component in place. The second portion of the prosthetic knee includes a lower tibial component, which in a manner similar to that of the femoral component, is secured to the upper surface of a tibia that has been prepared to receive the tibial component. The third portion of the prothesis is a patella member which would be of common construction. The tibial component typically includes an upper platform or portion having a pair of concavities shaped to receive in nested relation the curved surfaces of a pair of condyle shaped segments formed on the femoral component in order to provide an articulation surface. These components are positioned and shaped to duplicate as closely as possible the natural bending movement of the knee. The lower portion of the tibial component is necessarily secured to the upper portion of the prepared tibia so as to provide a firm base of contact between the tibial component and the tibia.
In securing the tibial component to the upper portion of the tibia it is important that the overall condition of the hard outer bone layer of the tibia is able to support the weight of the body. In the course of surgery, as the tibia is being prepared to receive the tibial component, the tibia is typically sculptured to include a flat upper face so that a lower surface of the tibial component can rest on the tibia face with optional further attachment through a post member that fits into the medullary canal of the tibia. Bone cement may be used to secure the post to the tibia.
One problem that confronts surgeons during this type of procedure, is that oftentimes the outer surface of the hard bone on the tibia has eroded away. The extent of this may not be fully realized by X-rays or pre-surgery examination and thus the surgeon is not aware of the extent of the problem until surgery is underway. At this time, the surgeon must make critical decisions during a limited period of time and affix the tibial component to the prepared tibial portion. However, if the upper outer or inner portion of the tibia is soft or has eroded, proper spatial placement of the tibial component would cause a space to develop between the lower surface of the component and the upper surface of the tibia.
In order to correct this situation during the limited time available, surgeons have in the past improvised by positioning a sliver of bone or a bone graft or a portion of cement in order to fill the gap between the hard surface of the tibia and the undersurface of the tibial component. Although both of these alternatives provide some support to the tibial component, neither of them operates to firmly secure the tibial component in place. Another alternative is to resect additional bone to a level below the bony defect upon which the component can be mounted. This procedure is not preferred because in some cases a shortening of the tibia to a certain degree results in a corresponding shortening of that particular leg of the patient.
Therefore, a need has arisen for an acceptable insert positioned between the upper surface of the tibia that has been eroded away and the tibial component to avoid having to remove additional bone from the tibia, and to maintain the tibial component in the same anatomical position for maximum registration with the femoral component after the knee joint has been reconstructed.